1. Field of the Invention
The invention relates to an ozone generator with a first and a second metallic electrode, with a layer of enamel on the surface of the second electrode facing the first electrode and a discharge gap between the first electrode and the enamel layer.
The invention thereby makes reference to a prior art such as arises, for example, from U.S. Pat. Specification No. 3,954,586.
2. Discussion of Background
For very many processes, extremely large quantities of ozone of the order of magnitude of hundreds of kilograms to ton per hour are necessary, and consequently they can be carried out virtually only if compact high-power ozone generators which can produce such high quantities of ozone are available.
To increase the power density of ozonizers--whether with the dielectric in the form of a tube or in the form of a plate--in the past the dielectric glass has been replaced by dielectrics based on plastic or ceramic.
In an ozone generator, the quantity of ozone Y formed per unit of discharge area is namely proportional to the electric power W per unit of area: EQU Y=K.multidot.W
In first approximation, the electric power W is in turn proportional to the relative dielectric constant E and inversely proportional to the thickness D of the dielectric: EQU W =K'.multidot.E/d
If glass is used as dielectric, the relative dielectric constant E is around 5. For reasons of stability, the wall thickness of such glass dielectrics must be at least 1.5 mm.
German Offenlegungsschrift 2,658,913 discloses an ozone generator which comprises a cooled internal electrode, an external electrode and a high-voltage electrode arranged concentrically in between, which are in each case coated on their outer circumferential surface with a glass-enamel dielectric. German Pat. Specification 2,534,033 discloses a high-frequency tube ozone generator in which a dielectric layer of silicate enamel or glass is applied to each of the opposite surfaces of concentrically arranged metal tubes. German Offenlegungsschrift 2,617,059 discloses the use of a thin silica gel layer as dielectric in ozone generators, which layer is applied to self-supporting metal electrodes.
German Offenlegungsschrift 2,354,209 discloses an ozone generator which consists of a self-supporting ceramic tube as dielectric, which is covered on its outer circumferential surface by a metal layer of an electrode and in which a metal tube is arranged concentrically as counter-electrode. However, such a self-supporting ceramic tube cannot be dimensioned just as thin as desired and is also very fragile.
German Offenlegungsschrift 2,065,823 discloses an ozone generator of which the electrodes consist of decarbonized steel, which are coated with a thin ceramic layer as dielectric. However, such ceramic layers have to be stoved at relatively high temperatures, which can result in a troublesome distortion of the self-supporting metal electrodes.
German Auslegeschrift 2,618,243 discloses a dielectric for ozone generators which consists of a ceramic material with Al.sub.2 O.sub.3, SiO.sub.2 and at least one alkaline metal oxide or alkaline earth metal oxide and has a dielectric constant between 5 and 10 and is 0.5 mm to 1 mm thick.
U.S. Pat. Specification No. 4,690,803 and German Offenlegungsschrift 3,128,746, for example, disclose ozonizers with plastic dielectric, in particular such ozonizers with titanium dioxide-filled plastic dielectric.
In the case of all the non-glass dielectrics described above, in principle the power density, and consequently the ozone yield, can be increased.
According to the findings of the applicant, the surface of the dielectric has a decisive influence on the efficiency. Dielectrics based on ceramic or synthetic resin are inferior to glass dielectrics in this respect.